Liquid-ring pumps of known type are disclosed in the inventors' U.S. Pat. No. 4,523,893 and GB patent publications 1 425 997 and 1 547 976. These liquid-ring pumps are advantageous for aspiration of centrifugal pumps and for the transport of gases, and for difficult pump media such as liquids mixed with or alternating with gases, foam, inhomogeneous polluting or particle-containing fluids, for volatile liquids such as acetone or in the transport of gases which require isothermic compression.
The above-mentioned publications describe a cylindrical internal surface which surrounds the rotor, and the rotor is disposed eccentrically in relation to the cylinder axis. Moreover, the arcuate inlet aperture is concentric with the axis of rotation and is smaller than the outlet aperture, which is concentric with the inside of the pump housing. During operation, the pump is partly filled with liquid which is hurled around in the housing under centrifugal force and forms a similarly cylindrical liquid ring with a certain thickness out from the surface. For reasons of the eccentric disposition of the rotor, only the edges of the blades are in contact with the liquid on the one side, and on the diametrically opposite side the liquid is in contact with the actual rotor hub by linear or surface contact, which is hereafter referred to as the sealing line or sealing surface. Between the blades there are thus formed several sickle-shaped cavities which extend around the rotor hub and are limited by the liquid ring, the blades and the rotor hub, and in which the gases are pumped forwards by the spiral movement of the rotor blades.
The eccentricity also results in the rotating liquid ring being, to a varying degree, in engagement with the rotor, and is therefore subject to accelerations and decelerations during the movement, where the speed of the liquid is at its lowest at the blades' most submersed position and greatest at that position in which only the outer parts of the blades are in the liquid. In other words, there occurs a deceleration of the liquid ring before the sealing line and an acceleration of the liquid ring after the sealing line. On that side on which a deceleration of the liquid occurs, there is a corresponding increase in its pressure simultaneously with a vortex formation. This pressure, the sealing pressure P1, is determinative for the amount of differential pressure that the pump is able to extend, in that it prevents gases from passing between the hub and the liquid ring against the pump direction. The point for P1 is shown in FIG. 1 of the drawing, where the reference FIG. 2 indicates the pump housing, 4 the blades, 6 the rotor hub, and 8 the liquid. It should be noted that the figure shows in principle a situation at a differential pressure of close to 0.
As a consequence of the sealing pressure, with the known pumps there arises a resulting radial force transversely to the rotational axis of the rotor, and which has to be absorbed in the rotor bearings. In some embodiments of this type of pump, it is desirable to house the rotor in bearings only at one end of the shaft, which limits the pump performance and necessitates a strong bearing construction.
The invention relates to a liquid-ring pump of the kind comprising a rotor provided with helical blades and which is suspended in bearings in a pump housing provided with an inlet aperture and an outlet aperture disposed at each end of the rotor. The distance between the outer diameter of the rotor blades and the inside surface of the housing facing towards the periphery of the rotor varies as seen along the circumference of the rotor. The said internal surface seen in a section at right-angles to the axis of rotation is configured as two or more substantially identical sectors where the rotor with its axis of rotation is placed symmetrically in relation to the sectors.
A such pump is known from U.S. Pat. No. 1,699,327. It is hereby possible to achieve two identical pressure distributions with two sealing pressures placed diametrically opposite around the rotor spindle, whereby the resulting power component transversely to the rotational axis of the rotor becomes zero. Such a pump construction provides the possibility of using a less robust and thus cheaper to manufacture spindle and bearing construction at the rotor, which is of particular significance for rotors which are suspended in bearings at only one end of the spindle.
In the line-shaped transition area between two adjacent sectors on the inner side of the pump housing the sealing surface develops a subpressure implying a danger of cavitation with subsequent damage to the wall of the housing.
The purpose of the present invention is to provide a pump of the known art where the cavitation risk is diminished and where other disadvantages resulting from the joint between the sectors are reduced. Another purpose is to provide anticavitation means that allow the pump housing to be made of semi-cylindrical shells in a simple and cheap way and with different mutual offset by the cylinder axes of the shells.
This purpose is fulfilled by a pump according to the invention of the type with the characteristic features that the internal surface at and seen in the direction of rotation immediately after the transition between adjoining sectors has a substantially plane portion which extends in a substantially tangential manner in relation to the rotor.
Preferred and advantageous embodiments of the pump according to the invention are disclosed.
If the internal surface at the inlet side is configured so that pulsations are suppressed and thus the capacity of the pump is hereby increased.
If the surface at the outlet end is configured as disclosed, the liquid ring is stabilized and a slightly smaller outlet opening is made possible than with pumps without this construction.
With the arrangement according to the invention, the vortex formation in the area with low liquid speed is increased, so that a static vortex arises in front of the place with the clearance reduction respectively the transverse wall portion. The sealing pressure is thus reinforced and the differential pressure can be increased, and the amount of rotating liquid is reduced with a consequent reduction in power consumption. When the pump is used as a liquid transport pump, i.e. almost or completely filled with liquid, the average speed of rotation of the liquid ring is low in relation to the speed of rotation of the rotor, and the use of this construction means that the convolutions function to a higher degree as a worm conveyor which conveys liquid from the suction side to the pressure side of the pump. Thus the achievable end-pressure, i.e. the maximum differential pressure achievable with volumetric flow equal to zero, will be close to theoretical velocity corresponding to the height of the liquid level which can be achieved at speeds equal to the peripheral speed of the rotor, see the equation h=v.sup.2 /2 g, where h is the height, v is the speed and g the gravitational force.
The pump according to the invention is used, among other things, for the transport of solid particles such as synthetic granulates in water. Providing that the specific gravity of the solid particles does not exceed approx. 1.5, this transport is effected without any problems, in that the vortices at the sealing surfaces force the particles in between the rotor blades, from where they are transported out through the discharge opening in the so-called pressure plate. When the specific gravity exceeds 1.5, there arises a tendency towards centrifugation, where the particles collect in a ring along the inner side of the rotor housing. This can be countered by placing carriers for the particles as disclosed by the invention.
In connection with the transport of particles, as suggested above the pumping-out of the particles is enhanced if the ends of the rotor and the housing are configured as a truncated cone, whereby the particles are conveyed as in a worm conveyor to the discharge opening, as presented by the invention.
With configurations of the pump in which the rotor does not end as truncated cone, the pump is used for tasks where the demands for the maximum differential pressure is limited to 200-300 mbar. The necessary sealing pressure is therefore correspondingly limited, and can consequently be achieved with a reduced amount of liquid with the hereto corresponding lower consumption of power. This is achieved by increasing the diameter of the discharge opening, which is the bore in the pressure plate, approximately corresponding to the diameter of the rotor hub, and at the same time provide a coverplate with a larger diameter than the rotor hub at the end of the rotor. During operation there is hereby created a rotating liquid lock, which ensures that the liquid ring is of such a thickness that at a differential pressure equal to zero it just touches the rotor hub.
In an embodiment of the invention there is provided extended blade portions at the outlet end of the rotor, the extensions stretching mainly perpendicularly to the axis of rotation of the rotor. Hereby an unwanted excessive liquid flow through the pump may be reduced.
With one embodiment, the result is that instead of being exposed to a strong braking effect, the liquid ring can deflect and continue into the cells, where it compresses the air which will always exist in the cells. Consequently, the cells come to serve as an accumulator for a part of the liquid ring's energy, which is released again when the liquid ring has passed the sealing line, and thus together with the less disturbed process of flow it contributes towards a smaller power requirement.
A particularly simple and inexpensive way in which to make the cells will appear from a description of the invention, in that the solid hub has a relatively small diameter, and therefore has relatively high blades between which there are disposed axial laminations of less height. The diameter across the outer edges of the laminations corresponds to the normal diameter of the hub.
Knives on the rotor hub for cutting large solid particles into lesser particles may be provided in a further embodiment of the invention.